1. Field of the Invention
The present invention relates to an apparatus and method for controlling a resonance frequency of an inverter refrigerator and, in particular, to an apparatus and method for controlling a resonant frequency of an inverter refrigerator whereby, in a compressor of an inverter refrigerator, when a current rotation frequency is converted to a target rotation frequency in the rotor detecting operation mode, an operation of the compressor is implemented in a frequency band higher or lower than a resonance frequency band.
2. Description of the Conventional Art
An inverter refrigerator rectifies a frequency(60 Hz) of an AC power source by a direct current and changes a supplied frequency(PWM) at the same time, whereby a rotation frequency of a compressor motor is adjusted and the amount of coolant compressed according to the adjusted frequency is controlled. Thus, in the case that there is much food in a refrigerator which food must be stored at a lower temperature as shown in FIG. 1, that is, in the case that the temperature in the refrigerator is higher than a set temperature, the rotation speed of a compressor is increased(usually, at a rotation frequency of higher than 60 Hz) for thereby taking much quantity of heat away. In the case that the amount of food is small or there is no food, that is, the temperature detected in the refrigerator is the same as the set temperature or is lower than the set temperature, the operation is performed at a lower speed(usually, at a speed of higher than 60 Hz) so that a small quantity of heat can be taken away from the foods, thereby reducing the energy consumed for compressing an unnecessary coolant.
The operation control of the compressor motor of the inverter refrigerator for performing the operation described above can be divided into three segments. As shown in FIG. 3, a first segment is an initial positioning mode for setting the rotor to a regular phase all the time by providing an electric current before starting the operation, a second segment is a synchronous operation mode for forcibly applying a current corresponding to a set starting torque, thereby accelerating the motor, because the initial rotation frequency of the motor is low and thus an induced electromotive force cannot be sensed, and a third segment is a rotor detecting operation mode for distributing a current appropriate for each phase of a stator according to a position information generated by an induced electromotive force and controlling the same when enough induced electromotive force can be detected based on an increased rotation frequency of the motor.
FIG. 2 is an example of a rotor position sensor of a conventional inverter refrigerator. The description thereof will be provided as follows.
There are two kinds of rotor position sensors; one is a hall sensor, and the other is a sensorless type. In a conventional inventor refrigerator motor, a stator 220 has an extra hall element for sensing an electric magnetic field when a magnet of a rotor 210 approaches the extra hall element. At present, the sensorless type is being generally used, considering a high pressure and current leakage in the compressor. The sensing principle thereof is that as a permanent magnet of the rotor is rotated near a coil wound on the stator 220, an induced electromotive force is generated at the coil based on the operation of an electric generator, thereby detecting the position of the rotor 210. In this way, the position of the rotor 210 is detected, whereby the current is flown to two phases(AB-BC-CA) of three phases(A, B, C) for sensing the induced electromotive force and supplying power, thus generating a rotation force, so that the rotor 210 is rotated.
FIG. 3 is a graph showing a frequency characteristic in the operation control mode of a compressor of a conventional inverter refrigerator. As shown in FIG. 2, the rotor 210 has a certain phase obtained by applying a current to three phases of the stator 220, respectively, for a certain time before starting the motor. The rotor is operated at the same phase for thereby obtaining a certain rotation. The above described operation is called as an initial positioning mode.
Thereafter, by selecting a starting pattern(a certain voltage and current), which is capable of generating a certain starting torque among a plurality of starting patterns according to the power voltage supplied when a start-up command signal is outputted to a semiconductor switching element having a certain phase, a current corresponding to the starting torque is supplied to thereby start the motor. Before performing the above starting operation, the rotor 210 must always be located at a certain position in the stator 210. The rotor 210 is located at a certain position based on an electric magnetic field formed by supplying a current corresponding to a certain phase of the stator. When the start-up operation is thusly prepared, a starting current is supplied for thereby driving the motor, so that the motor is operated in the synchronous operation mode.
Next, the rotor detecting operation mode will be described as follows referring to FIG. 4.
As shown in FIG. 3, when a transition segment is passed over, the position of the rotor is detected by a position detector 410 based on the induced electromotive force. The thusly detected position is outputted to a rotation frequency detector 440 to detect a rotation frequency. Then, the interior temperature of the refrigerator is judged by a set rotation frequency command unit 430 for thereby determining whether the rotor is operated at a lower RPM or a higher RPM. The current ratio supplied to each phase is differently set using a duty setting unit 450 according to a result of the determination. Six semiconductor switching elements each connected to a corresponding phase by a chopping signal generator 460 are controlled to thereby control the RPM of the compressor motor at a certain frequency.
In the above described conventional art, there is a problem that, as shown in FIG. 5, when an operating frequency passes through a frequency band in which a resonance occurs at the compressor or when the operating frequency is set in a resonance frequency band, the operating frequency is resonated, so that strong noises and vibrations occur.